package com.jerry.walking.utils;

import java.io.IOException;
import java.io.OutputStream;
import java.io.PushbackInputStream;

/**
 * 32 * This class implements a BASE64 Character decoder as specified in
 * RFC1521. 33 * 34 * This RFC is part of the MIME specification which is
 * published by the 35 * Internet Engineering Task Force (IETF). Unlike some
 * other encoding 36 * schemes there is nothing in this encoding that tells the
 * decoder 37 * where a buffer starts or stops, so to use it you will need to
 * isolate 38 * your encoded data into a single chunk and then feed them this
 * decoder. 39 * The simplest way to do that is to read all of the encoded data
 * into a 40 * string and then use: 41 *
 * <p/>
 * <pre>
 *    42    *      byte    mydata[];
 *    43    *      BASE64Decoder base64 = new BASE64Decoder();
 *    44    *
 *    45    *      mydata = base64.decodeBuffer(bufferString);
 *    46    *
 * </pre>
 * <p/>
 * 47 * This will decode the String in <i>bufferString</i> and give you an array
 * 48 * of bytes in the array <i>myData</i>. 49 * 50 * On errors, this class
 * throws a CEFormatException with the following detail 51 * strings: 52 *
 * <p/>
 * <pre>
 *    53    *    "BASE64Decoder: Not enough bytes for an atom."
 *    54    *
 * </pre>
 * <p/>
 * 55 * 56 * @author Chuck McManis 57 * @see CharacterEncoder 58 * @see
 * BASE64Decoder 59
 */

public class BASE64Decoder extends CharacterDecoder
{

    /**
     * This class has 4 bytes per atom
     */
    protected int bytesPerAtom()
    {
        return (4);
    }

    /**
     * Any multiple of 4 will do, 72 might be common
     */
    protected int bytesPerLine()
    {
        return (72);
    }

    /**
     * 74 * This character array provides the character to value map 75 * based on
     * RFC1521. 76
     */
    private final static char pem_array[] = {
            // 0 1 2 3 4 5 6 7
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', // 0
            'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', // 1
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', // 2
            'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', // 3
            'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', // 4
            'o', 'p', 'q', 'r', 's', 't', 'u', 'v', // 5
            'w', 'x', 'y', 'z', '0', '1', '2', '3', // 6
            '4', '5', '6', '7', '8', '9', '+', '/' // 7
    };

    private final static byte pem_convert_array[] = new byte[256];

    static
    {
        for (int i = 0;
             i < 255;
             i++)
        {
            pem_convert_array[i] = -1;
        }
        for (int i = 0;
             i < pem_array.length;
             i++)
        {
            pem_convert_array[pem_array[i]] = (byte) i;
        }
    }

    byte decode_buffer[] = new byte[4];

    /**
     * 103 * Decode one BASE64 atom into 1, 2, or 3 bytes of data. 104
     */
    protected void decodeAtom(PushbackInputStream inStream, OutputStream outStream,
                              int rem) throws IOException
    {
        int i;
        byte a = -1, b = -1, c = -1, d = -1;

        if (rem < 2)
        {
            throw new IOException("BASE64Decoder: Not enough bytes for an atom.");
        }
        do
        {
            i = inStream.read();
            if (i == -1)
            {
                throw new IOException();
            }
        } while (i == '\n' || i == '\r');
        decode_buffer[0] = (byte) i;

        i = readFully(inStream, decode_buffer, 1, rem - 1);
        if (i == -1)
        {
            throw new IOException();
        }

        if (rem > 3 && decode_buffer[3] == '=')
        {
            rem = 3;
        }
        if (rem > 2 && decode_buffer[2] == '=')
        {
            rem = 2;
        }
        switch (rem)
        {
            case 4:
                d = pem_convert_array[decode_buffer[3] & 0xff];
                // NOBREAK
            case 3:
                c = pem_convert_array[decode_buffer[2] & 0xff];
                // NOBREAK
            case 2:
                b = pem_convert_array[decode_buffer[1] & 0xff];
                a = pem_convert_array[decode_buffer[0] & 0xff];
                break;
        }

        switch (rem)
        {
            case 2:
                outStream.write((byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)));
                break;
            case 3:
                outStream.write((byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)));
                outStream.write((byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)));
                break;
            case 4:
                outStream.write((byte) (((a << 2) & 0xfc) | ((b >>> 4) & 3)));
                outStream.write((byte) (((b << 4) & 0xf0) | ((c >>> 2) & 0xf)));
                outStream.write((byte) (((c << 6) & 0xc0) | (d & 0x3f)));
                break;
        }
        return;
    }
}